Why are more stable carbocations faster formed?

[sludger13]

I have no idea how activation energy of a chemical reaction (in either direction) could depend on the thermodynamic stability of formed carbocation, as a product of that reaction. Activation energy of a chemical reaction should depend only on the structure of reagents, right?

The only thing I'm considering is that the more stable is a carbocation, the greater is the reaction enthalpy, thus it could (maybe) better heat the remaining reagents. And with greater Ek of that particles, then the reaction really run faster.

 

[sludger13]

Or, the structure of (1°, 2°, 3°) carbon substitueted REAGENTS really prevent
from elimination of carbocation differently...

 

[aroc91]

Activation energy isn't the only factor. The extent to which a reaction occurs is the sum total of the forward and reverse reactions, which happen continuously. Most everything can and does reverse spontaneously to a certain extent, which is dependent on the stability of the reactants and the products.

In the case of carbocations, the molecule separates into its constituent ions. With enough activation energy, they can reverse and reform the full compound. Repeat ad nauseum. Steric hindrance makes the reversal of 3° more difficult than the reversal of 2° and 1°, but it still happens to a certain extent. These relative amounts of hindrance, and therefore the rate of the reverse reaction, are what determine the overall forward rate.

That's how I came to understand it in my organic classes, which were close to 4 years ago now, so somebody else may be able to explain it better or point out if I happened to get something wrong.

 

[DrDu]

Activation energy is the difference in energy between the reactands and the transition state. The factors stabilizing the Carbocation are also important in the stabilization of the transition state which resembles more the carbocation than the neutral reactands.

 

[sludger13]

Activation energy is the difference in energy between the reactands and the transition state. The factors stabilizing the Carbocation are also important in the stabilization of the transition state which resembles more the carbocation than the neutral reactands.

This explanation seems fair to me, thanks.